This invention relates to means for reducing or dampening noise. In particular it relates to linings of the kind comprising an absorption layer which may be applied to a noise resonating surface.
Such linings are, for instance, in conventional use in the automotive industry where they are used to reduce the level of engine generated noise audible within the passenger compartment of automobiles. Thus, it is conventional to line noise resonating or reflecting surfaces, such as the interior surfaces of the sheet metal shell constituting the passenger compartment, with a layer of an elastic, preferably open-pored material capable of absorbing noise, and to seal or cover this layer by a cover layer, such as, for instance, carpeting.
Such linings are, particularly for certain frequency ranges, by and large performing satisfactorily. Tests have shown, however, that their effectiveness in absorbing or dampening noise commences at about 500 Hz and increases steadily with increasing frequencies. However, the noise spectrum of five or six cylinder internal combustion engines is such that within a range of from about 250 to about 650 Hz a particularly intense increase in wind noise as well as engine noise is discernible, i.e. in the very range in which conventional linings do not absorb or dampen noise generated by such engines in an optimal manner.
It is accordingly an object of the invention to provide a noise reduction lining having improved noise absorption or dampening properties.
A further object of the invention resides in the provision of a noise reduction lining effective for noise absorption in a relatively broad frequency range.
Still another object of the invention is to provide a noise reduction lining for use in automobiles powered by five or six cylinder internal combustion engines.
Another object of the invention is to provide a noise reducing lining being particularly effective in frequency ranges below 1 kHz.
A more particular object of the invention is to provide a noise reduction lining to absorb or dampen noise in the range characteristically generated by five or six cylinder engines.
Yet another object is to provide a noise reduction lining the increased cost of which is outweighed by the beneficial effect yielded by it.
Other objects will in part be obvious and will in part appear hereinafter.